1. Field of the Invention
The invention relates generally to a metallic or metal-coated housing, in particular for the air-bag control circuit of a motor vehicle, which provides shielding against radio-frequency radiation, having two housing sections, a printed circuit board mounted in the housing and supporting at least a part of a circuit, and a plug in the housing wall which makes via plug terminals the connection between the circuit, on the one hand, and electrical parts situated outside the housing, on the other hand, and which is already well known to the person skilled in the art, particularly one skilled in the art of motor-vehicle electronics.
The invention therefore relates to shielding circuits from RF (radio frequency) interference which acts on them from the outside. The invention also relates to the suppression of RF interference which originates from the circuit and acts on the environment.
2. Description of the Related Art
The invention was in fact initially developed for the air-bag system of a motor vehicle, which air-bag system is intended for installation in the steering wheel hub and is in accordance with Published PCT Application PCT/DE 90/00 423. It was found, however, that the invention can also be applied to other air-bag systems and even, in addition, also to all the other metallic or metal-coated housings which provide shielding against radio-frequency radiation.
In a known housing (as shown in German Utility Model 90 13 539) for shielding a circuit, a plug is provided in the housing wall. The plug is connected to the circuit by means of a connector. The housing of the plug is RF-shielded by a metal shield which surrounds it. The electrical contact to the housing is improved by spring tongues on the metal shield which press against the housing.
In this case, however, the connectors are not, or only partially, shielded inside the housing and may impair the circuit by RF radiation.
A further known housing (Research Disclosure, No. 313, May 1990, Emsworth, GB) has a lid and a base between which a printed circuit board supporting a circuit is clamped in the assembled state. The joints between the lid or base and the printed circuit board are coated with tin in order to improve the RF shielding action of the housing.
In this housing, too, the connectors which connect the plug to the printed circuit board are not shielded inside the housing and may impair the circuit as a result of HF (high frequency) radiation.
A particular problem in such housings, their plugs and their printed circuit boards (particularly in the case of air-bag systems) is the mass production and, in particular, that the components be as reliable and as easy as possible to produce and their subsequent assembly easy and reliable, but without the shielding action being allowed to suffer as a result.